Polyamide and polyimide have been developed as representatives of organic polymers having high-degree heat resistance. They form a large market in electronic device field, engineering plastic field such as automotive and aerospace uses, fuel cell field, medical material field, optical material field, etc. At their center, many various polymers are put into practical use, such as polyimide represented by nylon, KEVLAR, etc.; polyamide acid and polyimide, which can be representative heat-resistant polymers; polyamide imide, which is a composite of them; and polybenzoxazole, polybenzthiazole, polybenzimidazole, etc. In particular, polyimide is again recently attracting attention as a material that is resistant to a lead-free solder step.
Polymerization of many of these heat-resistant polymers is conducted by successively generating a reaction, such as polyaddition or polycondensation, using plural types of monomers having a bifunctional or trifunctional reactive group in the molecule.
Regarding combinations of monomers in polymerization, there are known, in the case of polyamide, a method in which a diamine-type monomer is condensed with a dicarboxylic acid derivative, such as dicarboxylic acid, acid chloride or ester, and, in the case of polyamide acid or polyimide, a method by a polyaddition of diamine and acid dianhydride. As diamines that are generally used, aliphatic diamines, alicyclic diamines and aromatic diamines have been reported. From the viewpoint of polymerizability and heat resistance, however, there is preferably used an aniline-series monomer that has a supporting skeleton of a benzene single ring, biphenyl-type or polycyclic structure, in which a plurality of benzene rings are directly or indirectly bonded together, and that contains a plurality of amines in the molecule. On the other hand, in the case of polybenzoxazole and polybenzthiazole, there are used monomers having amine and hydroxyl group and amine and thiol group at ortho-positions of the benzene ring.
The purpose of simultaneously having an amine and another functional group in the molecule is explained, as follows. That is, there is conducted a design in which diamine is used as a polymerization site and at the same time hydroxyl group and thiol group are used as functional groups for intramolecular condensation cyclization, and in which a phenolic acid group is contained as a photosensitive functional group of these alkali-soluble groups and the like. However, there are reports of only the above-mentioned limited combinations in an attempt to contain plural types of functional groups together with diamine.
On the other hand, fluoro compounds have been developed or put into practical use in wide material fields, such as polyolefins and condensation polymers, mainly in advanced material fields, due to characteristics possessed by fluorine, such as water repellency, oil repellency, low water absorptive property, heat resistance, weather resistance, corrosion resistance, transparency, photosensitivity, low refractive index property and low dielectric property. In the condensation polymer field, an attempt to introduce fluorine into a diamine monomer has been conducted. There are reports of a diamine monomer in which hydrogen of the benzene ring has been replaced with fluorine atom or trifluoromethyl group, a diamine monomer in which a hexafluoroisopropenyl group has been introduced between two aromatic rings, and a fluorine-containing diamine monomer in which the benzene ring has been subjected to a hydrogen reduction. Furthermore, a bishydroxyamine monomer having a hexafluoroisopropenyl group as a central atomic group and aromatic hydroxyamines at its both sides has also been put into practical use. In this case, it is applied as a polybenzoxazole or hydroxyl-containing polyimide.
They are explained, for example, as fluorine-containing polybenzazoles in Non-patent Publication 1, etc. On the other hand, there have recently been conducted active researches and developments on photoresist materials, in which transparency of fluoro compounds in ultraviolet region, particularly in vacuum ultraviolet region, has been applied. It is an attempt to achieve adhesion to substrate, high glass transition point, photosensitivity due to acidity of fluorocarbinol group, alkali development property, etc., while achieving transparency at each wavelength for use by introducing fluorine. In particular, of fluorocarbinols, hexafluoroisopropyl group attracts attention due to its dissolution behavior, non-swelling property, high contrast, etc., and many researches and developments are conducted.
As assumed from photoresist development examples, hexafluoroisopropyl group, which is an acidic alcohol, has a potential for achieving a rapid, homogeneous, alkali solubility, while it maintains less swelling property. There have been, however, few reports of development examples of heat resistant polymers using a similar concept, that is, heat resistant polymers containing a hexafluoroisopropyl group as an acidic alcohol. Carboxylic group can be cited as a general acidic group. However, due to its high reactivity with amine, they say that it is difficult to make an amine having a carboxylic group in the same molecule exist stably.
Non-patent Publication 1: “Latest Polyimide, its basic and application” edited by Japan Polyimide Study Group, page 426.